Newsletter  2021.1  Index

Theme : "Mechanical Engineering Congress, 2020 Japan (MECJ-20)” Preface Masaaki MOTOZAWA, Hideo MORI Pending Issues in Large-Eddy Simulation of Turbulent Flows Takeo KAJISHIMA (Osaka University) Unsteady Flows in Turbomachines (What We Should Know and How We Can Apply to Designing) Ken-ichi FUNAZAKI (Iwate University) Modeling of a Two-Phase Flow Simulation with the Evaporation of the Gas Diffusion Layer in a Polymer Electrolyte Fuel Cell Ryuya NAGAYAMA, Satoshi SAKAIDA, Kotaro TANAKA, Mitsuru KONNO (Ibaraki University) Statistical Mechanical Analysis of Nanoparticle Behavior for Measurement of Flow Velocity Distribution in Nanochannels by Particle Tracking Velocimetry Minori TANAKA (Keio University), Itsuo HANASAKI (Tokyo University of Agriculture and Technology), Yutaka KAZOE (Keio University) Memorandum Record of the 2020 JSME Annual Meeting -as a committee member of the web conference- Yasumasa ITO (Nagoya University)

 

Pending Issues in Large-Eddy Simulation of Turbulent Flows

Takeo KAJISHIMA Osaka University

Abstract

In the development of Large-Eddy Simulation (LES), the monumental ideas have been proposed decennially in the previous century: the eddy viscosity model by Smagorinsky (1963), the theory of filtering by Leonard (1974), the scale-similarity model by Bardina, et al. (1980) and the dynamic eddy-viscosity model by Germano, et al. (1991). The success of LES for turbulent flow in a plane channel with the wall-model by Deardorff (1970) and the non-slip boundary condition by Schumann (1975) created expectations of new trends in the numerical investigation of turbulent flows. In fact, LES has become a practical tool for the numerical simulation of turbulence in industry⁽¹⁾. On the other hand, essentially new idea is not found in this century. However, it does not mean there is not unsolved issue in LES. To enforce the nonslip boundary condition is still expensive especially for high Reynolds number conditions. For this issue, the refinement to treat the near-wall turbulence has been extensively conducted and there seems favorable developments recently.  More serious problem is involved in the basic equations. For example, the commutation of filtering and differentiation has been recognized from the beginning but it is still left neglected due to the mathematical difficulty. The imperfectness in the governing equation could become hidden barrier for the further development that including the application to multiphase flows that needs volume averages of multiple scales⁽²⁾. Meanwhile, the introduction of machine learning might be unavoidable in the LES modeling especially for the purpose obtaining a prompt answer. The necessity of physics-informed machine learning approach has been already pointed out. In addition, the necessity of properly volume-filtered equations should be reaffirmed as the basis of novel development.

Key words

Large-Eddy Simulation, Volume Filtering, Commutation Error, Turbulent Flow, Computational Fluid Dynamics

References

(1)	Kajishima, T. and Taira, K., “Computational Fluid Dynamics --- Incompressible Turbulent Flows”, Springer (2017).
(2)	Kajishima, T., “Immersed boundary/solid method for the numerical simulation of particle-laden flows”, Fluid Dynamics Res., Vol.51, No. 5 (2019), 051401.